The medical device industry produces a wide variety of electronic and mechanical devices such as neurological stimulators, therapeutic substance infusion pumps, pacemakers, and defibrillators for treating patient medical conditions such as pain, movement disorders, functional disorders, spastisity, cancer, and cardiac disorders. Medical devices can be configured to be surgically implanted or connected externally to the patient receiving treatment and can be used either alone or in combination with pharmaceutical therapies and surgery to treat patient medical conditions. For certain medical conditions, medical devices provide the best and sometimes the only therapy to restore an individual to a more healthful condition and a fuller life. One type of medical device is an implantable neurological stimulation system which typically includes a neurostimulator, an electrical stimulation lead, and an extension such as shown in Medtronic, Inc. brochure “Implantable Neurostimulation System” (1998). An implantable neurological stimulation system delivers electrical pulses to tissue such as neurological tissue or muscle to treat a medical condition.
One application of neurological stimulation systems is for spinal cord stimulation (SCS) to treat chronic pain. In many cases, the leads used for SCS are implanted percutaneously, through a large needle inserted into the epidural space. When a percutaneous lead is used for SCS, there can be undesirable current flow into areas of the patient's anatomy away from the spinal cord, because the electrodes typically cover the circumference of the stimulation lead. Additionally, dual percutaneous lead implants are becoming more common in the clinical practice of SCS. Currently, most dual lead systems are implanted as two individual single lead implants (i.e., two separate needle sticks, two separate lead insertions). Implanting dual leads in this way makes it difficult to control the relative position of the two leads with respect to one another. Currently, the physician typically uses fluoroscopy to determine the relative position of the two leads, and must try to assure that the leads do not touch (leading to a potential short between electrodes) and also that the leads are not too far apart (resulting in less than optimal stimulation). To prevent shorting, one approach has been to stagger the electrode contacts, rather than placing them adjacent on the parallel leads. In addition to being difficult to position at the time of implant, once the leads are permanently implanted, there is no guarantee that the leads will not move relative to one another (i.e., migrate) potentially reducing therapy efficacy.
For the foregoing reasons, what is needed is an electrode shield that can be attached to a stimulation lead to limit current flow to a selected area around the electrode, and a means for coupling more that one lead together in a controlled fashion.